Bio Atp help needed

[NokiaN95638]

Does anyone have bio mark schemes of 2002 and 2003.
and i need answers 2 dis questions:

http://www.xtremepapers.me/CIE/Cambridg ... qp_6_2.pdf

[ no. 2(B),(C),D) AND 3(C),]

 

[KarachiRocker]

Q2b. Start will be present in visking tube in tube A.
Reducing sugar will be present in both water and visking tube in B.
Q2c. Saliva contains enzyme Amylase which converts Starch to Maltase. Thus the solution contained reducing sugars which showed positive results with Benedict's Test.

 

[KarachiRocker]

c(ii) as maltose molecules are smaller than starch, they passes out of the semipermeable visking tube to the water in test tube by diffusion.

 

[KarachiRocker]

d(1) The test tube should be closed in order to prevent any loss of water by evaporation which may cause change in concentration.
2. Keeping tubes in water batch to keep constant temperature.

 

[intelnehalem]

Apparatus A:
Starch is present in the solution in the visking tubing. It is rightly absent in the test-tube. Reducing sugar is absent in both the solution in the tubing as well as in the water in the test tube.
Starch molecules are too large to pass through the partially permeable visking membrane which only allows small molecules such as glucose to pass through
Apparatus B:
Starch is absent in both the solution inside the tubing as well as in the water in the test tube. Reducing sugar is present in both the solution in the tubing as well as in the water in the test tube.

Reasons as to my answer for the solution in B and water in the test tube (B):
Saliva is added to the solution inside the visking tubing in B. saliva contains salivary amylase which breaks down starch to maltose. Due to this, concentration of starch gradually decreases hence it will not respond to the iodine test. Maltose is a reducing sugar and it is small enough to pass through the visking membrane, however not all of the reducing sugar diffuses out into the test tube. Once they both have equal concentrations of reducing sugar (maltose) , diffusion stops since there isn't a concentration gradient for reducing sugar molecules to diffuse
Water in the test-tube as well as the solution inside the tubing now contains reducing sugar , hence it will answer to the benedict's test but NOT TO THE STARCH TEST since starch molecules cannot diffuse out of the partially permeable membrane since they are large and only small molecules such as reducing sugars and water can pass through the membrane!


How to make this more accurate:
Same amount of starch solution has to be present in both A and B
Same amount of water has to be in the test tubes of A and B
Replication to reduce errors!
Same size of visking tubing has to be used
The temperature at which the experiment is carried out has to be kept constant